Method of manufacturing cationic acrylamide polymers, cationic acrylamide polymers, and the applications of these polymers

ABSTRACT

This invention provides cationic acrylamide polymers which are highly effective as paper strength agents, drainage agents and suspension flocculants, and which do not show much temporal deterioration; it also provides a method of manufacturing said polymers wherein the manufacturing equipment is compact and can be installed on site, and the cationicity of the polymers can be modified in a short time. 
     This invention comprises a method of manufacturing cationic acrylamide polymers by reaction, with a hypohalogenite, of a (meth)acrylamide homopolymer, a copolymer of (meth)acrylamide and acrylonitrile, a copolymer of (meth)acrylamide and N,N-dimethylacrylamide, in a high temperature range of 50°-110° C. for a short time; the polymers manufactured by said process; and paper strength agents, drainage agents and flocculants having these polymers as their principal constituent.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to a method of manufacturing cationic acrylamidepolymers mainly used as paper strength agents and flocculants, saidpolymers, and the applications of these polymers. More specifically, itrelates to cationic acryamide polymers obtained by carrying out aHofmann degradation reaction on acrylamide polymers at high temperaturefor a short time, their method of manufacture and the applications ofthese polymers.

(2) Description of the Prior Art

Examples of cationic acrylamide polymers (acrylamide polymers arehereafter referred to simply as polyacrylamides) known in the prior artare Hofmann decomposition polyacrylamides, Mannich polyacrylamides, andcopolymers of cationic monomers and acrylamides. Some of these polymershave various uses such as paper strength agents and flocculants, whilethe use of others is being considered.

Hofmann decomposition polyacrylamides have excellent properties notshared by Mannich polyacrylamides and copolymers of cationic monomers,however they lose their cationicity over a period of time in aqueoussolution, and their use has therefore been limited.

Various means have been considered to improve the characteristics ofthese polymers. One such means is to carry out the Hofmann decompositionof polyacrylamides at low temperature in order to suppress sidereactions and thereby suppress temporal deterioration. It is reportedfor example in "Kobunshi Ronbun", Vol. 33, No. 6, pp. 309-316, 1976,that in the Hofmann decomposition of polyacrylamides. substitution ofamino groups can occur easily even at low temperature due to thereaction promoting effect of neighboring groups, and it is alsodisclosed that to suppress side reactions (such as hydrolysis andformation of lactam rings) and depolymerizations, it is desirable tocarry out the reaction at a low temperature of the order of 25° C. orless to obtain amino-substituted PAM (polyacrylamides) with highperformance. The advantage of carrying out the Hofmann reaction ofpolyacrylamides at low temperature is also reported in JapaneseLaid-Open Patent Application Nos. 61-2001 03, 58-152004, 58-108206,57-65404, 55-6556, 52-152493 and 51-122188.

However, according to tests performed by the inventors of the presentinvention, it was found that merely carrying out the Hofmann reaction atlow temperature does not improve the temporal variation to such anextent as to permit commercial application of the polymers. In anotherapproach, hydroxylsubstituted compounds into which cationic groups havebeen substituted such as quaternary ammonium salts, or N,N-dialkylsubstituted diamines, guenidine and polyamines are also present when theHofmann decomposition is carried out, and these substances are made toreact with isocyanate intermediates of the Hofmann decomposition so asto incorporate them in the polymer, thereby preventing temporalvariation from occurring, as disclosed in Japanese Laid-Open PatentApplication Nos. 62-59602, 61-120807, 57-192408, 56-144295, 54-145790and 53-109594. According to the present inventors, however, thesemethods have still not given satisfactory results.

SUMMARY OF THE INVENTION

An object of this invention is to provide cationic acrylamide polymerswhich are highly effective as paper strength agents and suspensionflocculants, and cationic acrylamide polymers with little temporaldeterioration. Another object of this invention is to provide a methodof manufacturing said polymers wherein the reaction vessels are morecompact and can be installed on site, and the degree of cationicity canbe modified in a short time.

This invention is a method of manufacturing cationic acrylamide polymerswhich includes reaction of acrylamide polymers with a salt ofhypohalogenous acid (hereafter referred to as "hypohalogenite") underalkaline conditions in the temperature range 50-110° C. over a shortperiod of time (0.001 sec-10 min), and the cationic acrylamide polymersmanufactured by this method.

This invention is also a method of manufacturing cationic acrylamidepolymers which includes reaction of acrylamide polymers with ahypohalogenite under alkaline conditions in the temperature range50-110° C. over a short period of time (0.001 sec-10 min), wherein saidacrylamide polymers contain (a) 97-60 mol % of (meth)acrylamide units(97.7 -66.8 weight % of acrylamide, or 98.1-70.6 weight % ofmethacrylamide), and (b) 3-40 mol % of acrylonitrile units (2.3-33.2weight % in case of acrylamide and 1.9-29.4 weight % in case ofmethacrylamide).

This invention is also a method of manufacturing cationic acrylamidepolymers which includes reaction of acrylamide polymers with ahypohalogenite under alkaline conditions in the temperature range50-110° C. over a short period of time (0.001 sec-10 min), wherein saidacrylamide polymers contain (a) 97-60 mol % of (meth)acrylamide units97.7-66.8 weight % of acrylamide, or 98.1-70.6 weight % ofmethacrylamide), and (b) 3-40 mol % of N,N-dimethyl (meth)acrylamideunits (2.3-23.2 weight % in case of acrylamide and 1.9-29.4 weight % incase of methacrylamide).

It is preferable that after carrying out said reaction, reducing agentsare added or the temperature is lowered (50° C. or less) within a shorttime, or the pH is adjusted to 5 or less to stop the reaction.

It is also preferable that the reactants are added in alcohols, and thepolymers are precipitated.

This invention is also a drainage agent, paper strength agent orflocculant with said cationic acrylamide polymer as its principalcomponent, methods of using these agents in these applications, andpaper which has been strengthened by said polymers.

DETAILED DESCRIPTION OF THE INVENTION

In view of the above problems, the inventors considered the Hofmanndegradation of polyacrylamides in detail. It was found that cationicpolyacrylamides with far superior properties to Hofmann polyacrylamidesmanufactured by a low temperature reaction, and with propertiesequivalent to or better than cationic polyacrylamides manufactured by alow temperature reaction over a very long period time, could be obtainedby carrying out the Hofmann reaction at high temperature over a veryshort period of time, a result which had hitherto been totallyunexpected. This discovery led to the present invention.

This invention basically provides a method of manufacturing cationicacrylamide polymers characterized by reaction of acrylamide polymerswith a hypohalogenite under alkaline conditions in the temperature range50-110° C. over a short period of time (for example, 0.001 sec-10 min).

Further, this invention makes possible the design of a totally newsystem for manufacturing cationic polyacrylamides. The use of thismanufacturing system avoids problems of temporal deterioration ofHofmann degradation polyacrylamides, and opens up a wide range of newapplications.

This invention also provides a method of manufacturing a cationicpolyacrylamide copolymer obtained by reacting an acrylamide copolymercontaining (a) 97-60 mol % of (meth)acrylamide units, and (b) 3-40 mol %of acrylonitrile units, with a hypohalogenite under alkaline conditions;provides the polymer manufactured by this method; and provides astrength agent having this polymer as active constituent which increasespaper internal bond strength (the internal bond strength of the paperrefers to its strength in the direction of the thickness of the paper)and inter-layer paper strength.

The acrylamide copolymer used in this second invention is a Hofmannrearrangement product obtained by reacting an acrylamide copolymercontaining 3-40 mol of acrylonitrile units %, more preferably 5-30 mol %of acrylonitrile units, with a hypohalogenite under alkaline conditions.If the acrylonitrile groups account for less than 3 mol %, the effect ofacrylonitrile copolymerization is insufficient, that is the C.S.F.(Canadian Standard Freeness) value is not sufficiently large and thepaper internal bond strength is quite inadequate. If on the other handit exceeds 40 mol %, it interferes with water solubility so that theC.S.F. value and paper internal bond strength are even worse.

This invention also provides a method of manufacturing a cationicpolyacrylamide copolymer obtained by reacting an acrylamide copolymercontaining (a) 97-60 mol % of (meth)acrylamide units, and (b) 3-40 mol %of N,N-dimethyl (meth)acrylamide units, with a hypohalogenite underalkaline conditions; provides the copolymer manufactured by this method;and provides a paper strength agent having this copolymer as activeconstituent which increases paper internal bond strength and inter-layerpaper strength.

In this case, the acrylamide copolymer used is a Hofmann rearrangementproduct obtained by reacting an acrylamide copolymer containing 3-40 mol%, preferably 5-30 mol %, of N,N-dimethyl(meth)acrylamide units, with ahypohalogenite under alkaline conditions. If the N,N-dimethyl(meth)acrylamide units account for less than 3 mol %, the effect ofN,N-dimethyl (meth)acrylonitrile copolymerization is insufficient, thatis the C.S.F. value is not sufficiently large and the paper internalbond strength is quite inadequate. If on the other hand it exceeds 40mol %, it interferes with water solubility so that the C.S.F. value andpaper internal bond strength are even worse.

We shall now explain this invention in more detail.

The acrylamide polymer (polyacrylamide) used hereinafter in thisinvention means a homopolymer of an acrylamide (or methacrylamide), saidacrylamide copolymer of a (meth)acrylamide and acrylonitrile saidacrylamide copolymer of a (meth)acrylamide and a N,N-dimethyl(meth)acrylamide, a copolymer of an acrylamide (or methacrylamide) or ofan acrylamide copolymer with at least one type of unsaturated monomercapable of copolymerization, or a copolymer obtained by grafting onto awater-soluble polymer such as starch.

Examples of monomers capable of copolymerization are hydrophilicmonomers, ionic monomers or lipophilic monomers, one or more of whichmay be used. More specifically, examples of hydrophilic monomers arediacetone acrylamide, N,N-dimethyl methacrylamide, N-ethylmethacrylamide, N-ethyl acrylamide, N,N-diethyl acrylamide, N-propylacrylamide, N-acryloyl pyrolidine, N-acryloyl piperidine, N-acryloylmorpholine, hydroxyethyl methacrylate, hydroxyethyl acrylate,hydroxypropyl methacrylate, hydroxypropyl acrylate, various kinds ofmethoxypolyethyleneglycol (meth)acrylates, and N-vinyl-2-pyrolidone.

Examples of ionic monomers are acids such as acrylic acid, methacrylicacid, vinyl sulfonic acid, aryl sulfonic acid, methallyl sulfonic acid,styrene sulfonic acid, 2-acrylamide-2-phenylpropane sulfonic acid,2-acrylamide-2-methylpropane sulfonic acid and their salts, and aminessuch as N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethylmethacrylate, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminopropylmethacrylamide, N,N-dimethylaminopropyl acrylamide, and their salts.

Examples of lipophilic monomers are N-alkyl (meth)acrylamide derivativessuch as N,N-di-n-propyl acrylamide, N-n-butyl acrylamide, N-n-hexylacrylamide, N-n-hexyl methacrylamide, N-n-octyl acrylamide, N-n-octylmethacrylamide, N-tert-octyl acrylamide, N-dodecyl acrylamide andN-n-dodecyl methacrylamide; N-(ω-glycidoxyalkyl) (meth)acrylamidederivatives such as N,N-diglycidyl acrylamide, N,N-diglycidylmethacrylamide, N-(4-glycidoxybutyl) acrylamide. N-(4-glycidoxybutyl)methacrylamide, N-(5-glyoidoxypentyl) acrylamide, andN-(6-glycidoxyhexyl) acrylamide; (meth)acrylate derivatives such asmethyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate butyl,lauryl butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate and glycidyl(meth)acrylate; olefines such as methacrylonitrile, vinyl acetate, vinylchloride, vinylidene chloride, ethylene, propylene and butene; andstyrene, divinylbenzene, α-methyl styrene, butadiene and isoprene. Thequantity of unsaturated monomers used in the copolymerization depend ontheir types and combinations, but it is in the general range 0-50 weight%, and more preferably 0.01-50 weight %.

The water-soluble polymers with which said monomers are graftcopolymerized may be natural or synthetic. Examples of suitable naturalpolymers are starches of different origin and modified starches such asoxidized starch, carboxylated search. dialdehyde starch andcation-modified starch, cellulose derivatives such as methyl cellulose,ethyl cellulose, carboxymethyl cellulose and hydroxyethyl cellulose; andalginic acid, agar, pectin, carrageenan, dextran, pururan, arum root,Arabia rubber, casein and gelatin. Examples of suitable syntheticpolymers are polyvinyl alcohol, polyvinyl ether, polyvinyl pyrolidonepolyethylene imine, polyethylene glycol, polypropylene glycol,polymaleic acid copolymers, polyacrylic acid and polyacrylamides. Thequantity of said monomers to be added to the above water-solublepolymers is 0.1-10 times the quantity of the polymers.

Next, said monomers are polymerized to manufacture polyamrylamides, andit is preferable that the method used is radical polymerization. Thesolvent used may be a polar solvent such as water, alcohols ordimethylformamide, but as the Hofmann reaction is carried out in ansolution, polymerization in water solution is preferable. Theconcentration of monomer is 2-30 weight , preferably 5-30 weight %. Anyinitiator may be used provided it is water-soluble, and it is normallydissolved in an aqueous solution of the monomer. More specifically, itmay be a peroxide type such as ammonium persulfate, potassiumpersulfate, hydrogen peroxide or tert-butyl peroxide. The initiator maybe used alone, however it may also be used in conjunction with areducing agent as a redox type polymerizer. Examples of suitablereducing agents are sulfites, bisulfites, lower order ionized salts ofiron, copper and cobalt, organic amines such as N,N,N',N'-tetramethylethylenediamine and aniline, and reducing sugars such as aldose andketose.

Azo compounds may also be used such as hydrochlorides of2,2'-azobis-2-amidinopropane, 2,2'-azobis-2,4-dimethylyaleronitrile, and4,4'-azobis-4-cyanoyaleric acid or its salts. Further, two or more ofthe above polymerization initiators may be used in conjunction. Further,if a graft polymerization is carried out on water-soluble polymers,transition metal ions such as ceric ion and ferric ion may also be usedapart from said initiators, or in conjunction with them. The quantity ofinitiator added is usually 0.1-10 weight %, preferably 0.2-8 weight %based on the monomer. Further, in the case of a redox type initiator,the quantity of reducing agent added is usually 0.1-10.0%, preferably0.2-8.0%, on a molar basis.

The polymerization temperature when a single initiator is used is of theorder of 30-90° C.; when a redox type initiator is used, it is lower andof the order of 5-50° C. Further, there is no need to maintain thetemperature constant during the polymerization, and it may be variedconveniently as the reaction proceeds. In general, it rises due to theheat of polymerization which is liberated. Any atmosphere may be used inthe polymerization vessel, but in order to make the polymerizationproceed more rapidly, it is better to replace it with an inert gas suchas nitrogen. There is no particular limitation on the polymerizationtime, but it is of the order of 1-20 hours.

In this way a poly(meth)acrylamide is obtained. In the case of acopolymer of (meth)acrylamide units and acrylonitrile units, theacrylamide copolymer obtained is a water-soluble polymer containing97-60 mol % of (meth)acrylamide units, and 3-40 mol % of acrylonitrileunits. The viscosity of a 10% aqueous solution of this copolymer at 20°C. as measured by a Brookfield viscosimeter is 100-100,000 cps, butgenerally it preferably is in the range 100-80,000 cps. It is preferablyno less than 100 cps in order to attain a satisfactory performance,while on the other hand it is preferably no greater than 80,000 cps toprevent difficulty in handling and prevent gelation from occurringeasily.

In the case of a copolymer of (meth)acrylamide units andN,N-dimethyl(meth)acrylamide units, the acrylamide copolymer obtained isa water-soluble polymer containing 97-60 mol % of (meth)acrylamideunits, and 3-40 mol % of N,N-dimethyl(meth)acrylamide units. Theviscosity of a 10% aqueous solution of this copolymer at 20° C. asmeasured by a Brookfield viscometer is 100-100,000 cps, but generally itpreferably is in the range 100-80,000 cps. It is preferably no less than100 cps in order to attain a satisfactory performance, while on theother hand it is preferably no greater than 80,000 cps to preventdifficulty in handling and prevent gelation from occurring easily.

Next, a Hofmann decomposition reaction is carried out on thepolyacrylamide manufactured by the above method. In the case where themanufacture of the polyacrylamide starting material is carried out inaqueous solution, the solution may be used for the reaction withoutdilution or may be diluted if necessary. Further, in the case of a graftcopolymer, ungrafted polyacrylamide is also produced as a by-product,but usually this is not separated and is used for the reaction withoutmodification.

The Hofmann degradation is carried out under alkaline conditions, thatis, the hypohalogenite is made to act on the amide groups of thepolyacrylamide in the presence of an alkaline substance. Examples ofhypohalogenous acids are hypochlorous acid, hypobromous acid andhypoiodous acid. Examples of hypochlorite are alkali metal or alkalineearth metal salts of hypochlorous acid, and more specifically, sodiumhypochlorite, potassium hypochlorite, lithium hypochlorite, calciumhypochlorite, magnesium hypochlorite and barium hypochlorite. Similarly,examples of hypobromous acid salts and hypoiodous acid salts are alkalimetal and alkaline earth metal salts of hypobromous acid and hypoiodousacid. A halogen gas can also be bubbled into an alkaline solution togenerate the hypohalogenite.

Examples of suitable alkaline substances are alkali metal hydroxides,alkaline earth metal hydroxides and alkali metal carbonates. Of these,it is preferable to use an alkali metal hydroxide such as sodiumhydroxide, potassium hydroxide or lithium hydroxide. The quantity of theabove substances to be added to the polyacrylamide is, in the case ofthe hypohalogenite, usually 0.05-2 moles preferably 0.1-1.5 moles withrespect to amide groups, and in the case of the alkaline substance,usually 0.05-4.0 moles but more preferably 0.1-3.0 moles with respect toamide groups. Further, the molar ratio of the alkaline substances addedis 0.5-50, more preferably 0.1-10, and most preferably 1.5-5.0, based onthe hyphalogenite. In calculating this molar ratio, there is no problemif alkaline substances contained in the hypohalogenite are notconsidered. The range of alkalinity that is the range of pH, is about11-14. The alkalinity of the mixed solution of said hypohalogenite andalkaline substance, may be adjusted by adding a specified quantity ofhalogen to and reacting it with an aqueous solution of a specifiedconcentration of the alkaline substance. More specifically, an aqueouscaustic soda solution of sodium hypochlorite may be prepared by bubblinga specified quantity of chlorine gas into and reacting it with anaqueous solution of caustic soda of specified concentration. Thisreaction may be carried out under the normal conditions, there being nospecial restrictions.

Under the above conditions, the concentration of polyacrylamide is ofthe order of 0.1-17.5 weight %, however as stirring becomes difficultand gelation occurs easily when the reaction concentration increases, itis normally preferable that it is 0.1-10 weight %. Further, if thereaction concentration is less than 1%, the rate of the reaction isslow, and it is therefore more preferably 1-10 weight %.

The reaction temperature is usually in the range 50-110° C., preferably60-100° C.

In this invention, the Hofmann decomposition is then carried out in theabove temperature range for a short time. The reaction time may varydepending on the reaction temperature, and on the polymer concentrationof the reaction solution. As examples, when the polymer concentration isabout 1-10 weight %, it is sufficient to allow a reaction time of ten ormore minutes at 50° C., of several minutes at 65° C., and of severaltens of seconds at 80° C. If however the polymer concentration ishigher, the reaction is completed in a shorter time. Within the aboveconcentration range, the dependence of reaction time on reactiontemperature is expressed by the following two relations for reactiontime t. If the reaction is carried out within the specified limits, goodresults are obtained, and these limits is therefore respected: ##EQU1##where T is reaction temperature (° C.) and

    50≦T≦110

According to these relations between reaction time and temperature, thereaction time is 5.9 sec to 4.4 min at 50° C., and 4×10⁻³ sec to 35 secat 110° C. In the range 50-110° C., therefore, the reaction is carriedout for 0.001 sec to 10 min.

The number of cation equivalents of the cationic polyacrylamidemanufactured under the above conditions, when determined by colloidtitration at pH 2, is of the order of 0-10.0 meq/g, and by adjusting thequantity of hypohalogenite which is added, said number of equivalentscan be controlled. Further, as the r-action is carried out underalkaline conditions, the amide groups are also hydrolysed to producecarboxyl groups as by-products. The quantity of the by-products may beexpressed in terms of anion equivalents determined by colloid titrationat pH 10 , and is of the order of 0-10.0 meq/g. The quantity ofby-products can moreover be controlled by adjusting the quantity ofalkaline substance added.

After carrying out the reaction under the above conditions, in thisinvention, it is preferable that the reaction be stopped to suppress theprogress of side reactions. If however the product is to be used in theapplications described below immediately after the reaction, it is notessential to stop the reaction.

The reaction may be stopped by (1) adding a reducing agent, (2) coolingto a low temperature, or (3) lowering the pH of the solution by addingacid, these methods either being used independently or in combination.

In method (1), residual hypohalogenite is rendered inactive by reactionwith the reducing agent. Examples of suitable reducing agents are sodiumsulfite, sodium thiosulfate ethyl malonate, thioglycerol andtriethylamine. The quantity of reducing agent used is normally0.005-0.15 molar times, preferably 0.01-0.10 molar times, the quantityof hypohalogenite used in the reaction. In general, when a Hofmanndecomposition reaction is complete, residual compounds with activechlorine such as unreacted hypohalogenite remain. As these compounds cancause rusting of paper-making machines when said reaction solution isused as a paper strength agent, active chlorine is usually renderedinactive by a reducing agent. However, if the reaction is carried outwith a less molar equivalents of hypohalogenite than the number of molarequivalents of polyacrylamide units, and the reaction is moreovercarried out at high temperature practically no unreacted hypohalogeniteremains when the reaction is complete. If therefore these conditions arechosen, the solution may also be used as a paper strength agent withoutrendering the active chlorine inactive by means of a reducing agent.

In method (2), the progress of the reaction is suppressed by cooling,for example cooling by the use of a heat exchanger, or by diluting withcold water. The cooling temperature is normally no higher than 50° C.,preferably no higher than 45°C., and more preferably no higher than 40°C. There is no lower limit to the temperature, but it is preferable thatthe temperature be above the freezing point (-20° C.).

In method (3), the Hofmann decomposition is stopped by using acid tolower the pH of the solution which normally has an alkalinity of pH12-13 when the reaction is complete, and at the same time, the progressof hydrolysis reactions is stopped. The pH after addition of acid shouldbe no higher than neutral, and preferably in the range 4-6. Examples ofacids that may be used to adjust the pH are mineral acids such ashydrochloric acid, sulfuric acid, phosphoric acid and nitric acid, andorganic acids such as formic acid, acetic acid and citric acid. Any ofthese methods of stopping the reaction, (1)-(3), may be chosen dependingon the reaction conditions, and they may moreover also be used inconjunction.

In this invention, the reaction solution may, after the reaction hasbeen stopped by the above methods, be used as an aqueous solution of acationic polyacrylamide without modification. Alternatively, it may beintroduced into a solvent such as methanol which does not dissolvecationic polyacrylamide to precipitate the polymer, and the polymerdried to give a powder. Further, said aqueous solution of cationicpolyacrylamide obtained by the above method, may be stored in a tank,and used as necessary. In this case, the storage temperature should below without being low enough to freeze the aqueous solution, and shouldpreferably be in the range 10-15° C. If however it is to be used in arelatively short time, it may be stored at ambient temperature, and canthen be kept for about one month.

As described above, the cationic polyacrylamide of this invention can bemanufactured in a very short time, and the manufacturing equipment cantherefore be installed on site near where the polyacrylamide is to beused. This is an important advantage of the present invention. Further,if the reaction is carried out under conditions such that the quantityof hypohalogenite used is less than that of the amide groups of thepolyacrylamide, there will be no free hypohalogenous ions in thesolution. In this case, the solution can be added to, for example, pulpslurry without stopping the reaction.

The cationic polyacrylamide manufactured in this invention can beapplied to fields in which water-soluble cationic polymers are usuallyused, the main ones being those of chemical additives used inpaper-making or flocculants . As chemical additives, cationic polymersfind various applications in the paper-making process. The cationicpolyacrylamide manufactured by the method of this invention is used whenpulp is converted to paper. Its addition has a great effect in improvingdrainage when water is removed from the paper, and in increasing themechanical strength of the paper; in particular, it increases theinternal bond strength of the paper. In some cases, this effect can beenhanced by the concurrent use of water-soluble anionic resins. In thiscase, the water-soluble anionic resins that may be used are thosecontaining anionic substituent groups such as carboxyl, sulfonyl orphosphate, or heir salts, examples being anionic acrylamide resins,anionic polyvinyl alcohol resins, carboxymethyl cellulose,carboxymethylated starch and sodium alginate.

The method of using the cationic polyacrylamide of this invention as adrainage agent, may be a conventional method known to those skilled inthe art. The advantage of this invention, however, is that after thepolyacrylamide and hypohalogenite are reacted together at hightemperature for a short time as described above, they are added to thepulp slurry immediately. In this context, the meaning of the word"immediately" is that, either after the reaction has been stopped orwithout stopping the reaction, the aqueous solution after the reactionis not removed from the reaction pipes and run off to the outside, butis transported through the same pipes to be added to the pulp slurry.More specifically, the aqueous solution after reaction may be addeddirectly to the pulp slurry through the pipes, or a stock tank may beinstalled and, after temporary storage in the tank, the quantity addedmay be regulated. The time spent by the reaction solution in the pipesis not critical provided it does not deteriorate after the reaction. Ifhowever this time is too long, the equipment and piping required tostore the solution will necessarily be larger, and full benefit cannotbe derived from the advantages of this invention. To carry out thisinvention effectively, therefore, the solution is preferably addedwithin 5 hours, more preferably within 1 hour, and most preferablywithin 10 minutes after the reaction.

The solution may also be diluted with water depending on theconcentration of cationic polyacrylamide after reaction, and then added.The degree of dilution may vary according to the type of pulp and rateof paper-making, but the concentration of cationic polyacrylamide at thetime of addition is of the order of 0.1-10 weight %, preferably of theorder of 0.5-5 weight %, and more preferably 0.8-2 weight %. Thecationic polyacrylamide of this invention may be used alone, but it ispreferable if paper-making is carried out with the concurrent use ofaluminum sulfa&e and anionic resins as necessary. These chemicals may beadded in any desired order, or they may be added simultaneously.Further, the cationic polyacrylamide and water-soluble anionic resin maalso be added after mixing together at a pH of 9 or more. The additionratio of cationic polyacrylamide to water-soluble anionic resins may beany ratio desired within the range 100:0-10:90 in terms of solidweights. The quantities added is respectively 0.005-5 weight %,preferably 0.0-2 weight % based on dry weight of pulp solids. Theaddition may be carried out before the wet sheet is formed, normally ina location near the paper-machine wire parts. In this way, in thisinvention, the solution obtained immediately after the Hofmanndegradation reaction may be added to the pulp slurry either afterstopping the reaction or without stopping it. In both cases the solutionmay be added without dilution, but it is preferably added after dilutingit with water to 0.1-10% polymer solids as necessary.

The method of using the cationic polyacrylamide of this invention as apaper strength agent, may be a conventional method known to thoseskilled in the art. The cationic polyacrylamide of this invention may beused alone, but paper-making may be carried out with the concurrent useof aluminum sulfate and anionic resins as necessary. These chemicals maybe added in any desired order, or they may be added simultaneously.Further, the cationic polyacrylamide and water-soluble anionic resin mayalso be added after mixing together at a pH of 9 or more. The additionratio of cationic polyacrylamide to water-soluble anionic resins may beany ratio desired within the range 100:0-10:90 in terms of solidweights. The quantities added respectively 0.005-5 weight %, preferably0.01-2 weight % with respect to dry weight of pulp solids. The additionmay be carried out before the wet sheet is formed, but also after thelayered sheet, the addition may also be carried out by spray coating orroll coating. In this invention, a cationic polyacrylamide ismanufactured by the Hofmann decomposition of a polyacrylamide at hightemperature for a short time. The present inventors have found thesurprising fact that this cationic polyacrylamide shows far superiorpaper strengthening capability than the cationic polyacrylamide obtainedby carrying out the same reaction at low temperature for a long periodof time. The reason for this is not entirey clear. However if thepolyacrylamide is added to pulp slurry or the like without stopping thereaction, its effect is particularly marked, and from this it may beconjectured that N-chloro groups which are reaction intermediates orother functional groups produced by the high temperature contributedirectly or indirectly to paper strength. It is therefore more desirableto add the solution without stopping the reaction, however as thesolution deteriorates with time if the reaction is not stopped, it isdesirable to add it immediately after the reaction.

Paper manufactured by the above method has superior strength. Morespecifically, it has superior tear strength, internal bond strength, andcompressive strength. If therefore this method is employed, it will beextremely effective when used with raw materials containing a highproportion of waste paper beaten from corrugated board or newspaper, anda high strength paper may thus be obtained. It is not however limited tocorrugated board or newspaper, and can be used to manufacture paper withsuperior strength whenever such a paper is desired.

Moreover, an even better with internal bond strength, paper inter-layerstrength and drainage properties was achieved by using a cationicacrylamide polymer having a copolymer of (meth)acrylamide andacrylonitrile or a copolymer of (meth)acrylamide and N,N-dimethyl(meth)acrylamide as its principal constituent, as compared to a cationicacrylamide polymer having a homopolymer of (meth)acrylamide as itsprincipal constituent.

The cationic polyacrylamide manufactured by the method of this inventionis also useful as a flocculant for various kinds of waste water, and isparticularly effective in the flocculation and dewatering of organicsuspensions such as the raw sewage discharged as daily waste, wastewater, and excess sludges such as the activated sludge produced bybiotreatment. When the polyacrylamide of this invention is used as aflocculant for waste water and the like, the quantity added in terms ofsolid matter is usually 0.01-1,000 ppm, preferably 0.1-100 ppm, based onthe quantity of waste water, and either the flocculation andsedimentation method or the pressure flotation method may be used. Whenthe polyacrylamide of this invention is used as a dewatering agent forflocculated sediment and sludge, the quantity added as solid matter isusually 0.01-50 weight %, preferably 0.2-10 weight % based on the drysludge solids. In this case, an aqueous solution of the flocculant isusually added to the sediment or sludge in the flocculation tank and themixture stirred, or the two may be mixed directly in the pipe, to form aflow which is filtered off and dewatered. Various dewatering techniquesmay be employed such as vacuum dewatering, centrifugal dewatering usinga decanter or the like, capillary dewatering, or pressure dewateringusing a screw press dewaterer, filter press dewaterer or belt pressdewaterer.

Apart from the above applications, this invention may be used in a widevariety of other fields such as water-based paints, water-based films,microcapsules and oil drilling, and as a recovery agent, adhesive, fibertreatment agent, dye processing auxiliary agent or pigment dispersionagent, etc.

The cationic polyacrylamide obtained by the method of this invention, isnot only obtained in a short time, but in addition has a superior effectwhen applied in various industrial fields as has been described above,and as will also be clear from the following examples.

Although it need not be repeated, a cationic polyacrylamide of farsuperior quality can be manufactured at high temperature in a short-termreaction by the method of this invention, and it therefore evidentlyalso has the following effects:

(1) As the reaction time is very short, the reaction equipment can bemade lightweight and compact.

(2) As the reaction equipment can be made compact, it can be installedwhere the cationic polyacrylamide is used, and the reaction can be put"on line".

(3) A cationic polyacrylamide with a varying degree of cationicity canbe manufactured in a short time merely by varying the composition of thereaction solution.

(4) Paper with superior bond strength can also be manufactured.

EXAMPLES

We shall hereafter give some examples of this invention. It should benoted that % refers hereafter to weight % unless otherwise specified.

MANUFACTURING EXAMPLE 1

69.3 g of a 40% aqueous solution of acrylamide, 221.9 g of distilledwater and 6.5 g of isopropyl alcohol were introduced into 11 4-neckedflasks equipped with stirrers. reflux condensers, thermometers andnitrogen gas inlet tubes, and heated to 45° C. with stirring whilereplacing the atmosphere inside the flasks with nitrogen. Next, 0.34 gof a 10% aqueous solution of ammonium persulfate and 0.062 g of a 10%aqueous solution of sodium bisulfite were added, whereupon thepolymerization reaction began immediately and the temperature rose to65° C. Subsequently, the temperature was maintained at 65° C. for 2hours, whereupon an aqueous solution of polyacrylamide (PAM) containing10% of polymer and having a Brookfield viscosity of 5,500 cps at 25° C.,was obtained.

MANUFACTURING EXAMPLE 2

The same method as in Manufacturing Example 1 was used, except that thestarting materials were 63.9 g of a 40% aqueous solution of acrylamide,4.44 g of N-vinyl pyrroidone, 229.5 g of distilled water and 2.16 g ofisopropyl alcohol. An aqueous solution of a N-vinyl pyrrolidonecopolymer PAM containing 10% of polymer and having a Brookfieldviscosity of 4,800 ops at 25° C., was obtained.

MANUFACTURING EXAMPLE 3

The same method as in Manufacturing Example 1 was used, except that thestarting materials were 62.7 g of a 40% aqueous solution of acrylamide,4.91 g of N-acrylcyl pyrrolidine, 231.2 g of distilled water and 11.8 gof isopropyl alcohol. An aqueous solution of a N-acrylcyl pyrrolidinecopolymer PAM containing 10% of polymer and having a Brookfieldviscosity of 3,050 cps at 25° C., was obtained.

MANUFACTURING EXAMPLE 4

The same method as in Manufacturing Example 1 was used, except that thestarting materials were 70.6 g of a 40% aqueous solution of acrylamide,1.78 g of methacrylamide, 225.2 g of distilled water and 2.51 g ofisopropyl alcohol. An aqueous solution of a methacrylamide copolymer PAMcontaining 10 % of polymer and having a Brookfield viscosity of 7,000cps at 25° C., was obtained.

MANUFACTURING EXAMPLE 5

10.2 g of acrylamide and 1.67 g of styrene were dissolved in 200 ml ofdioxane in a 500 ml 4-necked flask equipped with a stirrer, refluxcondenser, thermometer and nitrogen gas inlet tube, and then heated to70° C. with stirring while replacing the atmosphere inside the flaskwith nitrogen. Next, a benzene solution of azobis isobutyronitrile wasadded. Stirring was continued at 70° C. for 4 hours, whereupon thesolution gradually became a white suspension, and a precipitate wasformed. After filtering the precipitate, it was dissolved in distilledwater, and methanol added to reprecipitate it. The Brookfield viscosityof a 10% aqueous solution of this polymer constituent was 1,200 cps at25° C.

MANUFACTURING EXAMPLE 6

The same method as in Manufacturing Example 1 was used, except that thestarting materials were 69.3 g of a 40% aqueous solution of acrylamide,2.30 g of acrylonitrile, 226.0 g of distilled water and 2.4 g ofisopropyl alcohol. An aqueous solution of an acrylonitrile copolymer PAMcontaining 10% of polymer and having a Brookfield viscosity of 9,400 cpsat 25° C., was obtained.

MANUFACTURING EXAMPLE 7

The same method as in Manufacturing Example 1 was used, except that thestarting materials were 64.9 g of a 40% aqueous solution of acrylamide,4.03 g of N,N-dimethylacrylamide, 228.6 g of distilled water and 2.49 gof isopropyl alcohol. An aqueous solution of a methacylamide copolymerPAM containing 10% of polymer and having a Brookfield viscosity of 7,800cps at 25° C., was obtained.

MANUFACTURING EXAMPLE 8

100 g of oxidized starch was dispersed in 900 g to distilled water in214-necked flasks equipped with stirrers, reflux condensers,thermometers and nitrogen has inlet tubes. After heating to 70-90° C. todissolve the starch completely, the solution was cooled to 20° C. 50 gof acrylamide, 445 g of distilled water and 5.0 g of isopropyl alcoholwere added, and nitrogen gas blown into the reaction solution withstirring for 30 min to completely replace the atmosphere inside theflasks. A solution of 4.5 g of ammonium cerium nitrate in 1N aqueousnitric acid was then added, and the reaction carried out at 20° C. for 1hour. After the reaction was complete, the solution was adjusted to pH6.5-7.0 with NaOH. The Brookfield viscosity of a 10% aqueous solution ofthis polymer constituent was 7,800 cps at 25° C.

EXAMPLE 1

Aqueous solution of the polyacrylamide polymers manufactured inManufacturing Example 1 was reprecipitated with 10 times their volume ofmethanol, and 1.0 g of the dried powdered polyacrylamide polymer wasdissolved in 14 g of distilled water. This solution was heated to 80°C., then a mixed solution containing 3.54 g of 12.5% sodium hypochloritesolution, 1.5 g of 30% sodium hydroxide solution, was added in oneinstallment with stirring. After the addition, 20 sec later, 80 g ofcool water (2-5° C.) was added to the reaction mixture, and the reactionwas stopped. A colloid titration was then carried out using a 1/400Naqueous solution of potassium polyvinyl sulfonate with toluidine blue asindicator, and the cationicity was measured. Table I shows the results.

EXAMPLES 2-4

The same operations as in Example 1 were carried out on thepolyacrylamide polymers manufactured in Manufacturing Examples 2-8 underreaction conditions of 80° C. for 5 sec, 65° C. for 60 sec and 50° C.for 180 sec, and the cationicity was measured in each case. Table Ishows the results.

COMPARATIVE EXAMPLES 1-2

The same operations as in Example 1 were carried out on thepolyacrylamide polymers manufactured in Manufacturing Examples 1-8 underreaction conditions of 20° C. for 180 sec and 20° C. for 5400 sec, andthe cationicity was measured in each case. Table I shows the results.

EXAMPLES 5-7

An aqueous solution of the polyacrylamide polymer manufactured inManufacturing Example 1 was reprecipitated with 10 times its volume ofmethanol, and 1.0 g of the dried powdered polyacrylamide polymer wasdissolved in 14 g of distilled water. This solution was maintained at80° C., then a mixed solution containing 3.54 g of 12.5% sodiumhypochlorite solution, 1.5 % of 30% sodium hydroxide solution, was addedin one installment with stirring. After the addition, the cationicitywas measured after 5, 20 and 60 sec by the same method as in Examples1-4. Table II shows the results.

COMPARATIVE EXAMPLES 3-6

An aqueous solution of the polyacrylamide polymer manufactured inManufacturing Example 1 was reprecipitated with 10 times its volume ofmethanol, and 1.0 g of the dried powdered polyacrylamide polymer wasdissolved in 14 g of distilled water. This solution was maintained at20° C., then a mixed solution containing 3.54 g of 12.5% sodiumhypochlorite solution and 1.5 g of 30% sodium hydroxide solution wasadded in one installment with stirring. After the addition, thecationicity was measured after 5, 10, 60 and 1800 sec by the same methodas in Examples 1-4. Table II shows the results

COMPARATIVE EXAMPLE 7

An aqueous solution of the polyacrylamide polymer manufactured inManufacturing Example 1 was reprecipitated with 10 times its volume ofmethanol, and 1.0 g of the dried powdered polyacrylamide polymer wasdissolved in 14 g of distilled water. This solution was maintained at80° C., then a mixed solution containing 3.54 g of 12.5% sodiumhypochlorite solution and 1.5 g of 30% sodium hydroxide solution wasadded in one installment with stirring. After the addition, thecationicity was measured after 1800 sec by the same method as inExamples 1-4. Table II shows the results.

EXAMPLE 8

An aqueous solution of the polyacrylamide polymer manufactured inManufacturing Example 1 was reprecipitated with 10 times its volume ofmethanol, and 1.0 g of the dried powdered polyacrylamide polymer wasdissolved in 34 g of distilled water. This solution was maintained at80° C., then a mixture of the quantities of 12.5% sodium hypochloritesolution and 30 wt% sodium hydroxide solution specified in Table III(molar ratio 1:2 and made up to 5 g with distilled water) was added inone installment with stirring. The cationicity was measured 20 sec afterthe addition by the same method as in Examples 1-4. Further, theanionicity was measured by adding a specified quantity of 1/200N methylglycol chitosane, and performing a back titration using a 1/400N aqueoussolution of potassium polyvinyl sulfonate with toluidine blue asindicator at a pH of 10.

EXAMPLE 9

An aqueous solution of the polyacrylamide polymer manufactured inManufacturing Example 1 was reprecipitated with 10 times its volume ofmethanol, and 1.0 g of the dried powdered polyacrylamide polymer wasdissolved in 34 g of distilled water. This solution was maintained at80° C., then a mixture of 3.54 g of a 12.5% sodium hypochlorite solutionand the quantity of 30 wt% sodium hydroxide solution with a molar ratioas specified in Table IV (made up to 5 g with distilled water) was addedin one installment with stirring. The cationicity was measured by thesame method as in Example 1, and the anionicity by the same method as inExample 8, 20 sec after the addition in each case.

PAPER-MAKING EXAMPLE 1

We shall refer to a 1% solution of cationic polyacrylamide prepared asin Example 1 and maintained at a temperature of no greater than 5° C.,as cationic polyacrylamide solution A. Aluminum sulfate was added to apulp slurry of Canadian Standard Freeness (referred to hereafter as CSF)of 480 ml and 1.0% concentration (electrical conductivity 1.2 ms)obtained by beating waste paper from corrugated board, in the proportionof 2.0% with respect to pulp (based on dry weights, hereafter same), andthe mixture stirred for 1 min. Next, a commercial anionic polyacrylamide(Hoplon 3150B, Mitsui Toatsu Chemicals Inc.) was added in the proportionof 0.24% with respect to pulp, and the mixture stirred for 1 min.Cationic polyacrylamide solution A was then added to the pulp slurry inthe proportion of 0.36% with respect to pulp, and stirring continuedafter the addition for 1 min. Part of the resulting pulp slurry wastaken to measure CSF according to the method described in JIS P8121, andthe remainder was used to make paper in a TAPPI standard sheet machine.The product was then dried in a hot air drier at 110° C. for 1 hour soas to obtain a hand-made paper with an areal weight of 125±3 g/m². Toevaluate this hand-made paper, its "specific rupture strength" wasmeasured according to JIS P8112, and its "internal bond strength" wasmeasured by a Kumagaya Riki Internal Bond Tester. Table V shows theresults.

PAPER-MAKING EXAMPLES 2-7

Paper-making tests were carried out by the same methods as inPaper-Making Example 1, excepting that the solutions of cationicpolyacrylamide manufactured in Examples 2-7 were used. Tables V and VIshow the results.

COMPARATIVE PAPER-MAKING EXAMPLE 1

Paper-making test was carried out by the same methods as in Paper-MakingExample 1, excepting that the reaction was carried out at 20° C. for 180sec. A hand-made paper with an areal weight of 125±3 g/m² was obtained.CSF, specific rupture strength and internal bond strength were measuredby the same methods as in Paper-Making Example 1.

Table VI summarizes these results.

COMPARATIVE PAPER-MAKING EXAMPLE 2

Paper-Making test was carried out by the same methods as in ComparativePaper-Making Example 1, except that the reaction was carried out at 20°C. 5400 sec. Table VI summarizes these results.

FLOCCULATION EXAMPLE 1

10 g of an aqueous solution of the polyacrylamide manufactured inManufacturing Example 1 (solids concentration 10 wt%) and 20 g ofdistilled water were heated to 80° C., then a mixed solution containing5.31 g of 12.5% sodium hypochlorite solution, 2.25 g of 30% sodiumhydroxide solution and 2.44 g of distilled water was added in oneinstallment. 10 sec after this addition, 10 ml of an aqueous solution of212 mg of sodium sulfite was added, the pH was adjusted to 4.5 withconcentrated hydrochloric acid, and the mixture was poured intoapproximately 10 times its volume of methanol to obtain a precipitate.After filtering the precipitate on a glass filter, it was dried in avacuum drier at 40° C. for 6 hours so as to obtain a white powder with acationicity of 7.98 meq/g. We shall refer to a 1% aqueous solution ofthis powder in distilled water as cationic polyacrylamide solution B.150 ml of raw sewage and sludge (digested sludge/excess sludge=1/3,solids 1.45%) was taken in a 300 ml beaker, 20 ml of cationicpolyacrylamide solution B was added, and the mixture stirred for 1 min.The resulting flocculent product was filtered in a Buchner funnel bynatural filtration (filter surface area 100 cm², filter cloth 60 meshTetron). The amount of filtrate collected from gravity dewatering wasmeasured at various time intervals, and found to be 106 ml after 10 sec,108 ml after 20 sec, 110 ml after 30 sec and 112 ml after 60 sec. Theflow remaining after gravity dewatering was centrifuged at 3000 rpm for5 min. and the water content of the dewatered cake obtained was found tobe 88%.

                                      TABLE I                                     __________________________________________________________________________                               Reaction Conditions (temperature/reaction                                     time)                                                                                         Cationicity                                                   Example         Comparative Example                Manu-                      1   2   3   4   1    2                             facturing                  80° C./                                                                    80° C./                                                                    65° C./                                                                    50° C./                                                                    20° C./                                                                     20° C./                Example                                                                            Acrylamide Polymer    30 sec                                                                            5 sec                                                                             60 sec                                                                            180 sec                                                                           180 sec                                                                            5,400 sec                     __________________________________________________________________________    1    PAM                   5.15                                                                              5.10    512 1.79 5.01                          2    5 mol % N-vinylpyrolidone copolymer                                                                 4.88                 4.82                          3    10 mol % N-acryloylpyrolidine copolymer                                                                 4.78    4.64     4.80                          4    5 mol % methacrylamide copolymer                                                                    4.96                                                                              4.81        1.76 4.98                          5    5 mol % styrene copolymer 3.64             3.66                          6    10 mol % acrylonitrile copolymer                                                                    5.07                                                                              5.02        1.65 5.18                          7    10 mol % N,N-dimethylacrylamide copolymer                                                           5.01                                                                              4.96        1.48 5.10                          8    50% acrylamide graft starch                                                                             2.73                                                                              2.80    0.91 2.82                          __________________________________________________________________________     Polymer concentration during reaction: 5 wt %                                 NaOCl concentration at time of addition: 0.28 mol/l                           NaOH concentration at time of addition: 0.56 mol/l                       

                                      TABLE II                                    __________________________________________________________________________                 Examples Comparative Examples                                                 5  6  7  3  4  5  6     7                                        __________________________________________________________________________    Reaction temperature (°C.)                                                          80 80 80 20 20 20 20    20                                       Reaction time (sec)                                                                        5  20 60 5  10 60 1,800 1,800                                    Cationicity (meq/g)                                                                        5.09                                                                             5.14                                                                             5.01                                                                             0.06                                                                             0.12                                                                             0.22                                                                             3.35  2.03                                     __________________________________________________________________________     Polymer concentration during reaction: 5 wt %                                 NaOCl concentration at time of addition: 0.28 mol/l                           NaOH concentration at time of addition: 0.56 mol/l                       

                                      TABLE III                                   __________________________________________________________________________    Quantity of NaOCl added,.sup.1                                                             10 mol %                                                                           20 mol %                                                                           30 mol %                                                                           50 mol %                                                                           100 mol %                                    Cationicity (meq/g)                                                                        1.29 2.58 3.89 5.73 7.88                                         Antionicity (meq/g)                                                                        0.25 1.30 1.70 0.95 0.72                                         __________________________________________________________________________     .sup.1 The quantity of NaOCl added is expressed in mol % based on the         acrylamide groups of the polyacrylamide                                       Reaction temperature: 80° C.                                           Reaction time: 20 sec                                                    

                  TABLE IV                                                        ______________________________________                                        NaOH/NaOCl (molar ratio)                                                                      4/1    2/1    0.8/1 0.6/1                                                                              0.4/1                                Cationicity (meq/g)                                                                           5.29   5.10   4.93  4.85 (1)                                  Anionicity (meq/g)                                                                            1.12   0.98   0.86  0.51 (1)                                  ______________________________________                                         (1) Gelation                                                                  Polymer concentration during reaction: 2.5 wt %                               NaOCl concentration at time of addition is fixed at 0.14 mol/l                Reaction temperature: 80° C.                                           Reaction time: 20 sec                                                    

                                      TABLE V                                     __________________________________________________________________________                                       Specific                                                                           Internal                              Paper-Making                       Rupture                                                                            Bond                                  Example                       CSF (ml)                                                                           Strength                                                                           Strength                              __________________________________________________________________________    1       PAM 80° C./20 sec                                                                            668  2.45 3.27                                  2       5 mol % N-vinylpyrrolidone copolymer                                                                670  2.48 3.23                                  6       10 mol % acrylonitrile copolymer                                                                    711  2.40 3.92                                  7       10 mol % N,N-dimethylacrylamide copolymer                                                           706  2.43 3.68                                  __________________________________________________________________________

                                      TABLE VI                                    __________________________________________________________________________    Reaction Condition (temperature/reaction time)                                               Paper-Making Examples                                                                     Comparative Paper-Making Example                                  3   4   5   1        2                                                        80° C./                                                                    65° C./                                                                    50° C./                                                                    20° C./                                                                         20° C./                                           5 sec                                                                             60 sec                                                                            180 sec                                                                           180 sec  5,400 sec                                 __________________________________________________________________________    CSF (ml)       660 658 665 502      635                                       Specific rupture strength                                                                    2.40                                                                              2.53                                                                              2.44                                                                              1.71     2.32                                      Internal bond strength (kg/cm)                                                               3.15                                                                              3.02                                                                              3.21                                                                              1.50     2.75                                      __________________________________________________________________________     Polymer concentration during reaction: 2.5 wt %                               NaOCl concentration at time of addition: 0.14 mol/l                           NaOH concentration at time of addition: 0.28 mol/l                            Papermaking conditions:                                                       Aluminum sulfate: 0.5%                                                        Anionic paper strength agents: 0.24%                                          Hofmann decomposition PAM: 0.36%                                              (each % based on pulp)                                                   

What is claimed is:
 1. A method of manufacturing a cationic acrylamidepolymer which comprises reacting an acrylamide polymer and ahypohalogenite under alkaline conditions at a pH of at least about 11for the specified short reaction time, t (sec); ##EQU2## where T isreaction temperature (° C.) and 50° C.≦T≦110° C.
 2. A method ofmanufacturing a cationic acrylamide polymer as in claim 1 which furthercomprises stopping the reaction in ten minutes after carrying out thereaction.
 3. A method of manufacturing a cationic acrylamide polymer asin claim 1 which further comprises stopping the reaction immediatelyafter carrying out the reaction.
 4. A method of manufacturing a cationicacrylamide polymer as in claim 1 which further comprises adding a watersoluble reducing agent immediately after carrying out the reactionwithin the specified reaction time t (sec).
 5. A method of manufacturinga cationic acrylamide polymer as in claim 4 wherein the reducing agentis selected from sodium sulfite, sodium thiosulfite, ethyl malonate,thioglycerol and triethylamine and the quantity of the reducing agentused is 0.005-0.15 molar times the quantity of hypohalogenite used inthe reaction.
 6. A method of manufacturing a cationic acrylamide polymeras in claim 1 which further comprises cooling to a temperature lowerthan 50° C. immediately after carrying out the reaction within thespecified reaction time t (sec).
 7. A method of manufacturing a cationicacrylamide polymer as in claim 1 which further comprises adjusting thepH to 5 or less immediately after carrying out the reaction within thespecified reaction time t (sec).
 8. A method of manufacturing a cationicacrylamide polymer as in claim 1 which further comprises precipitatingthe polymer by addition of the reaction product to alcohol which doesnot dissolve cationic polyacrylamide immediately after carrying out thereaction within the specified reaction time t (sec).
 9. A method ofmanufacturing a cationic acrylamide polymer as in claim 8 wherein thealcohol is methanol.
 10. A method of manufacturing a cationic acrylamidepolymer which comprises reacting an acrylamide polymer and ahypohalogenite under alkaline conditions at a pH of at least about 11for the specified short reaction time, t (sec); ##EQU3## where T isreaction temperature (° C.) and 50° C.≦T≦110° C., said copolymercontaining:(a) 97-60 mol % of (meth)acrylamide units (b) 3-40 mol % ofacrylonitrile units.
 11. A method of manufacturing a cationic acrylamidepolymer which comprises reacting an acrylamide copolymer and ahypohalogenite under alkaline conditions at a pH of at least about 11for the specified short reaction time, t (sec); ##EQU4## where T isreaction temperature (° C.) and 50° C.≦T≦110° C., said copolymercontaining:(a) 97-60 mol % of (b) 3-40 mol % ofN,N-dimethyl(meth)acrylamide units.